Characterization of a prototype strain of hepatitis E virus

Evolution of the hepatitis E virus hypervariable region

The presence of a hypervariable (HVR) region within the genome of hepatitis E virus (HEV) remains unexplained. Previous studies have described the HVR as a proline-rich spacer between flanking functional domains of the ORF1 polyprotein. Others have proposed that the region has no function, that it reflects a hypermutable region of the virus genome, that it is derived from the insertion and evolution of host sequences or that it is subject to positive selection. This study attempts to differentiate between these explanations by documenting the evolutionary processes occurring within the HVR. We have measured the diversity of HVR sequences within acutely infected individuals or amongst sequences derived from epidemiologically linked samples and, surprisingly, find relative homogeneity amongst these datasets. We found no evidence of positive selection for amino acid substitution in the HVR. Through an analysis of published sequences, we conclude that the range of HVR diversity observed within virus genotypes can be explained by the accumulation of substitutions and, to a much lesser extent, through deletions or duplications of this region. All published HVR amino acid sequences display a relative overabundance of proline and serine residues that cannot be explained by a local bias towards cytosine in this part of the genome. Although all published HVRs contain one or more SH3-binding PxxP motifs, this motif does not occur more frequently than would be expected from the proportion of proline residues in these sequences. Taken together, these observations are consistent with the hypothesis that the HVR has a structural role that is dependent upon length and amino acid composition, rather than a specific sequence.

Evolution of the hepatitis E virus polyproline region: order from disorder

The hepatitis E virus (HEV) polyproline region (PPR) is an intrinsically unstructured region (IDR). This relaxed structure allows IDRs, which are implicated in the regulation of transcription and translation, to bind multiple ligands. Originally the nucleotide variability seen in the HEV PPR was assumed to be due to high rates of insertion and deletion. This study shows that the mutation rate is about the same in the PPR as in the rest of the nonstructural polyprotein. The difference between the PPR and the rest of the polyprotein is due to the higher tolerance of the PPR for substitutions at the first and second codon positions. With this higher promiscuity there is a shift in nucleotide occupation of these codons leading to translation of more cytosine residues: a shift that leads to more proline, alanine, serine, and threonine being encoded rather than histidine, phenylalanine, tryptophan, and tyrosine. This pattern of amino acid usage is typical of proline-rich IDRs. Increased usage of cytosine also leads to >22% of all amino acids in the PPR being prolines. Alignments of PPR sequences from HEV strains representing all genotypes indicate that all zoonotic isolates share an ancestor, and the carboxyl half of the PPR is more tolerant of mutations than the amino half. The evolution of HEV PPR, in contrast with that of the rest of the nonstructural polyprotein, is molded by pressures that lead toward increased proline usage with a corresponding decrease in the usage of aromatic amino acids, favoring formation of IDR structures.

Hepatitis E virus in rats, Los Angeles, California, USA

This virus is unlikely to be a zoonotic threat.

The role of rats in human hepatitis E virus (HEV) infections remains controversial. A genetically distinct HEV was recently isolated from rats in Germany, and its genome was sequenced. We have isolated a genetically similar HEV from urban rats in Los Angeles, California, USA, and characterized its ability to infect laboratory rats and nonhuman primates. Two strains of HEV were isolated from serum samples of 134 wild rats that had a seroprevalence of antibodies against HEV of ≈80%. Virus was transmissible to seronegative Sprague-Dawley rats, but transmission was spotty and magnitude and duration of infection were not robust. Viremia was higher in nude rats. Serologic analysis and reverse transcription PCR were comparably sensitive in detecting infection. The sequence of the Los Angeles virus was virtually identical to that of isolates from Germany. Rat HEV was not transmissible to rhesus monkeys, suggesting that it is not a source of human infection.

The hepatitis E virus polyproline region is involved in viral adaptation

Genomes of hepatitis E virus (HEV), rubivirus and cutthroat virus (CTV) contain a region of high proline density and low amino acid (aa) complexity, named the polyproline region (PPR). In HEV genotypes 1, 3 and 4, it is the only region within the non-structural open reading frame (ORF1) with positive selection (4-10 codons with dN/dS>1). This region has the highest density of sites with homoplasy values >0.5. Genotypes 3 and 4 show ∼3-fold increase in homoplastic density (HD) in the PPR compared to any other region in ORF1, genotype 1 does not exhibit significant HD (p<0.0001). PPR sequence divergence was found to be 2-fold greater for HEV genotypes 3 and 4 than for genotype 1. The data suggest the PPR plays an important role in host-range adaptation. Although the PPR appears to be hypervariable and homoplastic, it retains as much phylogenetic signal as any other similar sized region in the ORF1, indicating that convergent evolution operates within the major HEV phylogenetic lineages. Analyses of sequence-based secondary structure and the tertiary structure identify PPR as an intrinsically disordered region (IDR), implicating its role in regulation of replication. The identified propensity for the disorder-to-order state transitions indicates the PPR is involved in protein-protein interactions. Furthermore, the PPR of all four HEV genotypes contains seven putative linear binding motifs for ligands involved in the regulation of a wide number of cellular signaling processes. Structure-based analysis of possible molecular functions of these motifs showed the PPR is prone to bind a wide variety of ligands. Collectively, these data suggest a role for the PPR in HEV adaptation. Particularly as an IDR, the PPR likely contributes to fine tuning of viral replication through protein-protein interactions and should be considered as a target for development of novel anti-viral drugs.

Isolation and characterization of two new hepatitis E virus genotype 1 strains from two mini-outbreaks in Lahore, Pakistan

BACKGROUND

Pakistan is a highly endemic area for hepatitis E virus (HEV) infection. The aim of the current study was to isolate and characterize strains of HEV in two mini outbreaks.

RESULTS

RNA was extracted and reverse transcribed to cDNA. Nested PCR was done for the detection of HEV RNA. The positive bands were eluted, cloned in TA vector and sequenced in both directions using genetic Analyzer (Applied Biosystem Inc, USA). Phylogenetic analysis was done using MEGA4 software. We isolated two new HEV genotype-1 strains from Lahore, Pakistan, based on cloning and sequencing of ORF2 region.

CONCLUSIONS

Our study suggest that both the human HEV strains were closely related to the Sar-55 but different from the Abb-2B and 87-Pakistan-B HEV isolates sharing 88-91% sequence identity to Pakistani isolate Sar-55. These results indicated that Sar-55 is the main endemic HEV strain in various areas of the country.

Advances in immunology of hepatitis E virus infection

Hepatitis E virus (HEV) is the cause of human hepatitis E. Hepatitis E is endemic in many developing countries, including China, and represents a major public health problem. In this article, we will review the current knowledge on humoral and cellular immune responses and mechanisms of immunologic injury in HEV infection as well as the development of HEV vaccines.

Imported and autochthonous hepatitis E virus strains in Spain

Hepatitis E virus (HEV) causes hepatitis E, an acute liver disease displaying diverse epidemiological patterns that correlate with the genetic diversity of the virus. Only a few strains have been characterized to date from cases of hepatitis E in Spain. Using three sets of new, HEV-specific primers, viral genome fragments were amplified from serum samples from 13 patients with acute hepatitis in different regions of Spain. Direct sequencing of these fragments and analysis of sequences lead to identify six genotype 1, six genotype 3, and one genotype 4 viral strains. Genotype 1 sequences were found in the clade with subtype 1a strains, and were amplified from travelers from India and Bangladesh, and from an African immigrant. Genotype 3 sequences were found in the clade with subtype 3f strains, were always amplified from patients who did not travel abroad recently, and were closely related to sequences from swine strains isolated in Spain. Patients infected by these strains lived in different regions and were mainly men aged above 50 years. The single genotype 4 sequence detected was amplified from a traveler returning from Vietnam. Hepatitis E is both an imported and an autochthonous disease in Spain, and closely related HEV genotype 3f strains are responsible for infections acquired locally in different regions of the country within a given time. Studies involving a significant number of human, swine, and environmental viral strains collected prospectively are, however, required in order to confirm a swine origin for autochthonous HEV genotype 3 human infections.

Acute hepatitis E virus infection in Taiwan 2002-2006 revisited: PCR shows frequent co-infection with multiple hepatitis viruses

Sporadic cases of acute hepatitis E virus (HEV) infection with production of anti-HEV IgM have been reported occasionally in Taiwan despite no reported outbreaks in the past. This study was undertaken to determine whether serological markers correlated with virus detection. From 2002 to 2006, 72 reported cases of acute hepatitis E seropositive for anti-HEV IgM in Taiwan were enrolled for investigation. Acute phase serum samples were collected for detection of HEV RNA, HBV DNA, HCV RNA, and GBV-C RNA by PCR. The results showed that viral sequences of HEV, HBV, HCV and GBV-C were detected in 54 (75%), 21 (29.2%), 9 (12.5%), and 22 (30.6%) of cases, respectively. Acute hepatitis A co-infection was excluded in all patients because none were seropositive for anti-HAV IgM and, nine patients (12.5%) did not seroconvert to anti-HEV IgG. These results suggest that serum markers did not correlate completely with viremia in the diagnosis of acute HEV infection. Multiple viruses may co-infect with acute hepatitis E virus in Taiwan. Detection of hepatitis E viremia together with seropositivity for anti-HEV IgM and followed by seroconversion to anti-HEV IgG should be included in the diagnostic criteria for HEV infection.

Full-genome nucleotide sequence and analysis of a Chinese swine hepatitis E virus isolate of genotype 4 identified in the Guangxi Zhuang autonomous region: evidence of zoonotic risk from swine to human in South China

BACKGROUND

Hepatitis E virus (HEV) is one of the leading causes of the enteric-transmitted acute hepatitis. Many studies have found high identities between human and animal HEV isolates using partial sequence comparison analysis.

AIMS

To determine and phylogenetically analyse the complete genome of the swGX40 isolate from the Guangxi Zhuang autonomous region.

METHODS

The overlapping fragments of HEV isolate swGX40 were amplified with reverse transcription-nested polymerase chain reaction (PCR) and the 5' and 3' ends of viral genome were amplified with rapid amplification of cDNA ends. The PCR products were cloned and sequenced. The sequence and phylogenetic analysis of swGX40 were performed.

RESULTS

The full genome of the swGX40 strain consisted of 7233 nucleotides, excluding the poly (A) tail of 36 residues. There are three open reading frames (ORFs), encoding 1705, 674 and 114 amino acids (aa) respectively. The full-genomic sequencing showed that the swGX40 strain shared similarity with all known HEV genotype 1, 2 and 3 isolates by 73.4-76.5% and with an identity of 83.1-91.2% among genotype 4 HEV isolates. The partial ORF2 sequencing (249 nt) showed that swGX40 shared a high nucleotide identity of 94 and 97% with the Chinese human strain LZ-105 and the Vietnamese human strain HE-JVN-1 respectively.

CONCLUSIONS

The swine isolate swGX40 was closely related to the human isolate LZ-105, both of which were collected from Liuzhou, the same district in the Guangxi Zhuang autonomous region. This molecular biological evidence strongly supported the zoonosis hypothesis of hepatitis E.

Molecular epidemiology of hepatitis E virus in Hong Kong

Hepatitis E virus (HEV) is one of the major causes of acute and self-limiting hepatitis in human. In Hong Kong, the number of notifications increased from 26 to 62 from year 2001 to 2007. This study describes the molecular epidemiology of HEV in Hong Kong in order to determine the movement and distribution of HEV. HEV in 171 serum samples from HEV IgM positive cases from year 2001 to 2007 were amplified using RT-PCR and subjected to nucleotide sequencing. Phylogenetic analysis showed 162 of 171 HEV detected cases (94.7%) belonged to genotype IV and 8 (4.7%) to genotype I. Interestingly, a cluster of 10 cases in year 2007 that had the same sequence of HEV was identified. Epidemiological data however did not detect any relationship between these cases. Since zoonotic transmission is a well known route of HEV infection, close monitoring of the circulating HEV strains in human and food source animals may help to provide additional information on the transmission of HEV and possible source of infection in Hong Kong.

Hepatitis E: a complex and global disease

Thirty years after its discovery, the hepatitis E virus (HEV) continues to represent a major public health problem in developing countries. In developed countries, it has emerged as a significant cause of non-travel-associated acute hepatitis. HEV infects a wide range of mammalian species and a key reservoir worldwide appears to be swine. Genomic sequence similarity between some human HEV genotypes and swine HEV strains has been identified and we know that humans can acquire HEV infection from animals. Although for the most part the clinical course of HEV infection is asymptomatic or mild, significant risk of serious disease exists in pregnant women and those with chronic liver disease. In addition, there are data on the threat of chronic infections in immunocompromised patients. Beyond management of exposure by public health measures, recent data support that active immunisation can prevent hepatitis E, highlighting the need for vaccination programmes. Here we review the current knowledge on HEV, its epidemiology, and the management and prevention of human disease.

Deletions of the hypervariable region (HVR) in open reading frame 1 of hepatitis E virus do not abolish virus infectivity: evidence for attenuation of HVR deletion mutants in vivo

Hepatitis E virus (HEV) is an important human pathogen, although little is known about its biology and replication. Comparative sequence analysis revealed a hypervariable region (HVR) with extensive sequence variations in open reading frame 1 of HEV. To elucidate the role of the HVR in HEV replication, we first constructed two HVR deletion mutants, hHVRd1 and hHVRd2, with in-frame deletion of amino acids (aa) 711 to 777 and 747 to 761 in the HVR of a genotype 1 human HEV replicon. Evidence of HEV replication was detected in Huh7 cells transfected with RNA transcripts from mutant hHVRd2, as evidenced by expression of enhanced green fluorescent protein. To confirm the in vitro results, we constructed three avian HEV mutants with various HVR deletions: mutants aHVRd1, with deletion of aa 557 to 585 (Delta557-585); aHVRd2 (Delta612-641); and aHVRd3 (Delta557-641). Chickens intrahepatically inoculated with capped RNA transcripts from mutants aHVRd1 and aHVRd2 developed active viral infection, as evidenced by seroconversion, viremia, and fecal virus shedding, although mutant aHVRd3, with complete HVR deletion, was apparently attenuated in chickens. To further verify the results, we constructed four additional HVR deletion mutants using the genotype 3 swine HEV as the backbone. Mutants sHVRd2 (Delta722-781), sHVRd3 (Delta735-765), and sHVRd4 (Delta712-765) were shown to tolerate deletions and were infectious in pigs intrahepatically inoculated with capped RNA transcripts from the mutants, whereas mutant sHVRd1 (Delta712-790), with a nearly complete HVR deletion, exhibited an attenuation phenotype in infected pigs. The data from these studies indicate that deletions in HVR do not abolish HEV infectivity in vitro or in vivo, although evidence for attenuation was observed for HEV mutants with a larger or nearly complete HVR deletion.

Cross-protection of hepatitis E virus genotypes 1 and 4 in rhesus macaques

The purpose of this study was to determine cross-protection between HEV genotypes 1 and 4, which are prevalent in China. Fecal suspensions of genotypes 1 and 4 from patients, as well as genotype 4 from swine, were inoculated intravenously into rhesus macaques. Each inoculum contained 5 x 10(4) genome equivalents of HEV. After infection, serum and fecal samples were collected serially and the levels of alanine aminotransferase (ALT) and anti-HEV IgG and IgM in sera, and HEV RNA in fecal samples, were measured. Liver biopsies were carried out. All the infected monkeys (12/12) developed anti-HEV IgG and exhibited fecal shedding of virus. IgM was detected in 11 of 12, and ALT elevation occurred about 2-6 weeks post-inoculation in 10 of 12, infected monkeys. Hepatic histopathology was consistent with acute viral hepatitis and the ORF2 antigen of HEV was detected in the granular cytoplasm of hepatocytes by immunohistochemistry. After recovery from their initial HEV infection, the monkeys were challenged with a heterologous genotype or heterologous source of HEV and monitored for hepatitis and fecal shedding. Previous infection with HEV completely or partially protected against subsequent challenge with a heterologous virus, because 7 of 11 monkeys did not develop HEV infection or shed virus in the feces, and none of them developed hepatitis or exhibited ALT elevation or liver biopsy findings of hepatitis. In conclusion, previous HEV infection may give rise to cross-genotype and cross-host-species protection.

Hepatitis E virus: molecular virology, clinical features, diagnosis, transmission, epidemiology, and prevention

Hepatitis E virus (HEV), the sole member of the genus Hepevirus in the family of Hepeviridae, is the major cause of several outbreaks of waterborne hepatitis in tropical and subtropical countries and of sporadic cases of viral hepatitis in endemic and industrialized countries. Transmission of HEV occurs predominantly by the fecal-oral route although parenteral and perinatal routes have been implicated. The overall death rate among young adults and pregnant women is 0.5-3% and 15-20%, respectively. HEV is a small non-enveloped particle that consists of a polyadenylated single-strand RNA molecule containing three discontinuous and partially overlapping open reading frames. There are four major genotypes of HEV and a single serotype. At present, there are approximately 1,600 sequences of HEV that are already available at INSDC of both human and animal isolates. Diagnostic and molecular assays have been described for the accurate differentiation of ongoing from remote infection of HEV. Identification and characterization of swine HEV in the United States, Japan, and many other countries and their close relationship to locally characterized human HEV found in the same geographic areas prove that HEV is indeed a zoonotic virus and that domestic swine, wild deer, and boars are reservoirs of HEV in nature. A cell culture system for the propagation of the virus has been described, and a very successful phase 2 vaccine trial has been completed. This review summarizes the current knowledge on the molecular biology, clinical features, transmission, diagnosis, epidemiology, and prevention of HEV.

Hepatitis E vaccine

Hepatitis E is an emerging disease in resource-poor regions of the world. It is estimated that about 2 billion people live in areas endemic for this disease. The inability to reproducibly culture hepatitis E virus makes it impossible to develop traditional live or inactivated vaccines. However, significant progress has been made in developing and testing recombinant subunit vaccines based on the viral capsid protein. This review summarizes these efforts.

Mutations within potential glycosylation sites in the capsid protein of hepatitis E virus prevent the formation of infectious virus particles

Hepatitis E virus is a nonenveloped RNA virus. However, the single capsid protein resembles a typical glycoprotein in that it contains a signal sequence and potential glycosylation sites that are utilized when recombinant capsid protein is overexpressed in cell culture. In order to determine whether these unexpected observations were biologically relevant or were artifacts of overexpression, we analyzed capsid protein produced during a normal viral replication cycle. In vitro transcripts from an infectious cDNA clone mutated to eliminate potential glycosylation sites were transfected into cultured Huh-7 cells and into the livers of rhesus macaques. The mutations did not detectably affect genome replication or capsid protein synthesis in cell culture. However, none of the mutants infected rhesus macaques. Velocity sedimentation analyses of transfected cell lysates revealed that mutation of the first two glycosylation sites prevented virion assembly, whereas mutation of the third site permitted particle formation and RNA encapsidation, but the particles were not infectious. However, conservative mutations that did not destroy glycosylation motifs also prevented infection. Overall, the data suggested that the mutations were lethal because they perturbed protein structure rather than because they eliminated glycosylation.

Hepatitis E virus

Hepatitis E virus (HEV) is the aetiological agent of non-HAV enterically transmitted hepatitis. It is the major cause of sporadic as well as epidemic hepatitis, which is no longer confined to Asia and developing countries but has also become a concern of the developed nations. In the Indian subcontinent, it accounts for 30-60% of sporadic hepatitis. It is generally accepted that hepatitis E is mostly self-limited and never progresses to chronicity. It has a higher mortality in pregnant women where the disease condition is accentuated with the development of fulminant liver disease. Currently, no antiviral drug or vaccine is licensed for HEV, although a vaccine candidate is in clinical trials. HEV genome is 7.2kb in size with three open reading frames (ORFs) and 5' and 3' cis acting elements, which have important roles to play in HEV replication and transcription. ORF1 codes for methyl transferase, protease, helicase and replicase; ORF2 codes for the capsid protein and ORF3 for a protein of undefined function. HEV has recently been classified in the genus Hepevirus of the family Hepeviridae. There are four major recognised genotypes with a single known serotype. The absence of a reliable in vitro propagation system is an obstacle to deciphering HEV biology. The genome of HEV has been cloned, sequenced and the infectious nature of these replicons has been established. However, questions related to replication, transcription, virus-host interactions and pathogenesis remain to be answered. This comprehensive review summarises the progress made so far in HEV research, and addresses some of the unanswered questions.

Evaluation of human (genotype 1) and swine (genotype 4)-ORF2-based ELISAs for anti-HEV IgM and IgG detection in an endemic country and search for type 4 human HEV infections

Open reading frame 2 proteins (ORF2) from swine (genotype 4, S-ORF2) and human (genotype 1, H-ORF2) hepatitis E virus (HEV) having 91.4% identity at amino acid level were expressed using baculovirus expression system. Comparison of ELISAs based on the two proteins yielded identical results when sequential serum samples from monkeys and pigs experimentally infected with genotypes 1 and 4 HEV, respectively, were tested. Samples from patients (n = 258) suffering from non-A, non-B hepatitis during outbreaks of the disease and 180 sera from apparently healthy children were screened by H-ORF2-, S-ORF2-based ELISAs and Genelabs ELISA, a widely used commercial test for HEV diagnosis. Specificity of all three tests in detecting IgM and IgG antibodies in healthy children was comparable. Excellent correlation was noted in detecting both IgM (98.7% concordance) and IgG (97.7% concordance) anti-HEV antibodies when H-ORF2 and S-ORF2 ELISAs were compared. When compared with Genelabs ELISA, both H-ORF2 and S-ORF2 ELISAs identified 34 and 18 additional positives, respectively, in IgM and IgG anti-HEV tests showing comparatively less sensitivity of the commercial assay. The concordance of Genelabs ELISA in IgM detection was 86.4% and 85.6%, respectively, with H-ORF2 and S-ORF2 ELISAs. The concordance between Genelabs ELISA and H-ORF2 decreased further to 73.6% when 129 human samples from recent HEV epidemics (2002-2004) were tested for IgM. Similar results were obtained when sequential samples from 11 hepatitis E patients were examined. Screening of serum samples from 137 sporadic non-A, non-B hepatitis cases further confirmed the superiority of the H-ORF2 and S-ORF2 ELISAs. All 36/137 HEV-RNA-positive samples from sporadic cases belonged to genotype 1 confirming absence/rarity of type 4 human infections. H-ORF2 and S-ORF2 antigens were swappable in ELISAs for detecting both genotypes 1 and 4 HEV infections.

Genetic variability and evolution of hepatitis E virus

Hepatitis E virus (HEV) is the sole member of the genus Hepevirus in the family Hepeviridae. HEV is transmitted primarily by the fecal-oral route, and water-borne epidemics are characteristic of hepatitis E in many developing countries in Asia, Africa and Latin America where sanitation conditions are suboptimal. Accumulating lines of evidence indicate that HEV-associated hepatitis also occurs domestically among individuals in industrialized countries, that there are animal reservoirs of HEV such as domestic pigs and wild boars, and that hepatitis E is a zoonosis. Based on the extensive genomic variability among HEV isolates, HEV sequences have been classified into four genotypes: genotype 1 consists of epidemic strains in developing countries in Asia and Africa; genotype 2 has been described in Mexico and several African countries; genotype 3 HEV is widely distributed and has been isolated from sporadic cases of acute hepatitis E and/or domestic pigs in many countries in the world, except for countries in Africa; and genotype 4 contains strains isolated from humans and/or domestic pigs exclusively in Asian countries. This paper reviews current knowledge on the genomic variability, geographic distribution and zoonotic aspects of HEV as well as the clinical significance of genotype and evolution of HEV.

Detection of hepatitis E virus in liver, mesenteric lymph node, serum, bile and faeces of naturally infected pigs affected by different pathological conditions

The objective of the present study was to detect hepatitis E virus (HEV) in different samples from naturally infected pigs and to characterise genetically the detected strains. Serum, bile, liver, lymph nodes and faeces of 69 animals from 1 week to 4 months of age with different pathological conditions were collected. Reverse transcriptase-polymerase chain reaction (RT-PCR) to detect HEV and histopathology of tissues was conducted. Positive RT-PCR samples were sequenced and phylogenetically analysed. HEV was detected in at least one sample in 26 out of 69 animals (37.7%). Bile was the most frequently positive sample, followed by mesenteric lymph nodes, liver, faeces and serum. HEV was detected in pigs of 1 (n = 7), 2 (n = 8) and 3 (n = 11) months of age. A total of 22 of 69 (31.9%) pigs had mild to moderate hepatitis and 15 of them were HEV RT-PCR positive in at least one of the tested samples. The highest sensitivity of viral detection was achieved using samples that cannot be obtained from live pigs, such as liver, mesenteric lymph node and bile. Phylogenetic analyses confirmed that all Spanish swine HEV strains detected belonged to genotype III. Therefore, genotype III strains are present in a relative high proportion of pigs between 1 and 3 months of age. Through this study, it cannot be ruled out if concomitant infections may influence the distribution of HEV in infected pigs.

Characterization of hepatitis E virus from outbreak and sporadic cases in Turkmenistan

Large outbreaks and sporadic cases of hepatitis E have been reported in Central Asia. We assessed the genetic relatedness of hepatitis E virus (HEV) strains from outbreak and sporadic cases in Turkmenistan. Specimens from outbreak and sporadic cases of acute hepatitis non-A, non-B were tested by reverse transcription (RT)-polymerase chain reaction (PCR) to identify the presence of HEV RNA; nucleotide sequences were analyzed. HEV RNA was detected from 23/156 (15%) outbreak cases and 2/23 (9%) sporadic cases. The HEV outbreak isolates represented 14 unique sequences with genetic distances varying between 0.3% and 8.6%, 12 of which were closely related, with distances between 0.3% and 5.6%. Two unique sequences from outbreak cases 32 and 42 were closely related (99.7%) and shared 91.8-93.4% of sequence with the other 12 strains. The two strains were closely related to the previously published isolates from Burma (99.7-100%) and India-Madras (95.7-96.1%). The two 1994 sporadic HEV strains were 97.4% distinct, wile revealing 91.4-94.1% homology to 1985 strains, and 94.4-94.7% to HEV from the neighboring China and Pakistan. Genetic diversity of HEV that caused the hepatitis E outbreak in Turkmenistan in 1985 suggests heterogeneity of viral sources. Sporadic hepatitis E that occurred in 1994 was caused by viral strains genetically distinct from those causing the outbreak in 1985, yet closely related to HEV from neighboring countries. The study suggests that circulation of a broad variety of strains of HEV may occur in Central Asia, regardless of international borders, presenting a significant public health threat to the population of the region.

Molecular detection and sequence analysis of a new hepatitis E virus isolate from Pakistan

Sporadic and epidemic acute viral hepatitis E in many developing countries is caused by hepatitis E virus (HEV). The HEV genome has been classified into three major genotypes. However, extensive diversity has been noted among HEV isolates from patients with acute hepatitis in China and Taiwan. Some reports indicated that multiple genotypes of HEV could cocirculate in the same area; even distinct genotypes of HEV could exist in the same patient. Pakistan is a highly endemic area for hepatitis E. So far only two Pakistan HEV isolates Sar-55 (87-Pakistan-A) and Abb-2B (88-Pakistan-2B) have been characterized, and the nucleotide sequences of these two HEV isolates show only 90% homology. In this study, a third HEV isolate from Pakistan (87-Pakistan-B) is reported. The sequences of a 438-bp fragment from ORF-2 and a 259-bp fragment from the ORF-1-3 region of this new HEV isolate were obtained and sequenced. The sequence analysis showed that this new HEV isolate was very closely related to the Sar-55 but different from the Abb-2B HEV isolate. These results indicated that the Sar-55 (87-Pakistan-A) genotype is the main endemic HEV strain in the Sargodha area. These data will be useful for HEV epidemiological studies, diagnosis and vaccine development.

Positive reactions on Western blots do not necessarily indicate the epitopes on antigens are continuous

Epitope mapping (identification of an antigenic site recognized by an antibody) is an important component of vaccine development and immunological assays. It is widely accepted that in Western blots, antibodies react exclusively with continuous epitopes: discontinuous epitopes are assumed to be irreversibly destroyed by electrophoresis under the denaturing conditions used for sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Here, we demonstrate that the epitopes recognized by four different monoclonal antibodies were identified as discontinuous epitopes when characterized by radioimmunoprecipitation assays and enzyme-linked immunosorbent assays, yet each of these antibodies reacted with the corresponding antigen on Western blots. Reaction on Western blots may be due to epitope renaturation during or after the transfer of the protein to a membrane. Therefore, positive reactions on Western blots do not necessarily indicate that epitopes are continuous and this caveat should be kept in mind while characterizing them.

Phylogenetic analysis of hepatitis E virus isolates in southern China (1994-1998)

BACKGROUND

We have previously reported the identification of divergent hepatitis E virus (HEV) isolated (G9, G20 and 93G) in Guangzhou, a city in southern China. They are now recognised as a new HEV subgenotype in the world. However, the relatedness and significance of these novel isolates in sporadic HEV infection in southern China is still unclear.

OBJECTIVES

To perform phylogenetic analysis of nucleotide sequences from 41 HEV isolates in southern China from 1994 to 1998.

STUDY DESIGN

The partial nucleotide sequence of the HEV isolates were determined and compared with reported sequences in the GenBank. Their relatedness was analysed using computer software.

RESULTS

The majority of the HEV isolates, 39 out of 41, were found to belong to the Burmese-like isolates (genotype 1). The other two belonged to the Guangzhou-like isolates. The latter were only found in the samples collected in 1994. They, together with the G9 isolate, form a unique tree located between genotype 1 and genotype 4 (divergent HEV strains from northern China and Taiwan) on the phylogenetic tree.

CONCLUSION

Our results suggest that the Burmese-like isolates are the main causative agents of sporadic HEV infection in southern China. The Guangzhou-like isolates, which appeared transiently in 1994, did not seem to adapt to the environment and have caused no sporadic infection since.

Phylogenetic analysis of global hepatitis E virus sequences: genetic diversity, subtypes and zoonosis

Nucleotide sequences from a total of 421 HEV isolates were retrieved from Genbank and analysed. Phylogenetically, HEV was classified into four major genotypes. Genotype 1 was more conserved and classified into five subtypes. The number of genotype 2 sequences was limited but can be classified into two subtypes. Genotypes 3 and 4 were extremely diverse and can be subdivided into ten and seven subtypes. Geographically, genotype 1 was isolated from tropical and several subtropical countries in Asia and Africa, and genotype 2 was from Mexico, Nigeria, and Chad; whereas genotype 3 was identified almost worldwide including Asia, Europe, Oceania, North and South America. In contrast, genotype 4 was found exclusively in Asia. It is speculated that genotype 3 originated in the western hemisphere and was imported to several Asian countries such as Japan, Korea and Taiwan, while genotype 4 has been indigenous and likely restricted to Asia. Genotypes 3 and 4 were not only identified in swine but also in wild animals such as boar and a deer. Furthermore, in most areas where genotypes 3 and 4 were characterised, sequences from both humans and animals were highly conserved, indicating they originated from the same infectious sources. Based upon nucleotide differences from five phylogenies, it is proposed that five, two, ten and seven subtypes for HEV genotypes 1, 2, 3 and 4 be designated alphabetised subtypes. Accordingly, a total of 24 subtypes (1a, 1b, 1c, 1d, 1e, 2a, 2b, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 4a, 4b, 4c, 4d, 4e, 4f and 4g) were given.

Hepatitis E virus genotyping based on full-length genome and partial genomic regions

Some genomic regions for hepatitis E virus (HEV) genotyping have been reported to correlate well with the results from the phylogenetic analyses on the basis of the complete genome. However, few studies have systemically investigated the genomic regions for HEV genotyping using a combined phylogenetic and statistical approach. A consensus region for HEV genotyping has not been determined. In this study the nucleotide identities and genetic distances of 24 partial genomic regions and the complete genome sequences of 37 HEV strains were compared statistically. It was demonstrated with both one-way ANOVA and two-way ANOVA that only one genomic region in RNA-dependent RNA polymerase domain (4254-4560nt) for which there were no significant differences when compared with the full-length genome (P>0.05). The same four genotypes were identified by phylogenetic analysis based on this statistically predicted region identified as for the complete genome. RT-PCR amplification of HEV strains from all four genotypes confirmed conservation of the flanking primer sites of this region. Serum samples from 20 patients with a clinical diagnosis of hepatitis E were further analyzed by PCR using the same primers, 13 were positive and could be classified into genotype 4. These data strongly suggested that this newly identified region could be used for future HEV genotyping.

The 41-amino-acid C-terminal region of the hepatitis E virus ORF3 protein interacts with bikunin, a kunitz-type serine protease inhibitor

Hepatitis E virus (HEV), a human plus-stranded RNA virus, contains three open reading frames (ORF). Of these, ORF1 encodes the viral nonstructural polyprotein, ORF2 encodes the major capsid protein, and ORF3 codes for a phosphoprotein of undefined function. Recently, using the yeast two-hybrid system to screen a human cDNA liver library, we have isolated and characterized AMBP (alpha1-microglobulin/bikunin precursor), which specifically interacts with the ORF3 protein of HEV. The ORF3 protein expedites the processing and secretion of alpha1-microglobulin. When checked individually for interaction, the second processed protein from AMBP, bikunin, strongly interacted with the full-length ORF3 protein. This protein-protein interaction has been validated by immunoprecipitation in both COS-1 and Huh7 cells and by His6 pull-down assays. In dual-labeling immunofluorescent staining, followed by fluorescence microscopy of transfected human liver cells, ORF3 colocalized with endogenously expressed bikunin. Finally, a 41-amino-acid C-terminal region of ORF3 has been found to be responsible for interacting with bikunin. The importance of this virus-host protein-protein interaction, with reference to the viral life cycle, has been discussed.

Hepatitis E viruses in humans and animals

Hepatitis E virus (HEV) is an emerging pathogen belonging to a newly recognized family of RNA viruses (Hepeviridae). HEV is an important enterically transmitted human pathogen with a worldwide distribution. It can cause sporadic cases as well as large epidemics of acute hepatitis. Epidemics are primarily waterborne in areas where water supplies are contaminated with HEV of human origin. There is increasing evidence, however, that many animal species are infected with an antigenically similar virus. A recently isolated swine virus is the best candidate for causing a zoonotic form of hepatitis E. The virus is serologically cross-reactive with human HEV and genetically very similar, and the human and swine strains seem to be cross-infective. Very recent evidence has also shown that swine HEV, and possibly a deer strain of HEV, can be transmitted to humans by consumption of contaminated meat. In this review, we discuss the prevalence, pathogenicity, diagnosis and control of human HEV, swine HEV, the related avian HEV and HEV in other hosts and potential reservoirs.

Evidence of recombination between divergent hepatitis E viruses

Phylogenetic and recombination analysis was performed on 32 complete hepatitis E virus (HEV) genomes from infected humans and pigs. For the first time, evidence for recombination between divergent HEV strains was obtained, with at least two strains being found to have discordant phylogenetic relationships consistent with the occurrence of intragenotype recombination. This finding confirms that humans can be dually infected with divergent HEV strains and has implications for the emergence and evolution of new HEV epidemics.

In vitro and in vivo mutational analysis of the 3'-terminal regions of hepatitis e virus genomes and replicons

Hepatitis E virus (HEV) replication is not well understood, mainly because the virus does not infect cultured cells efficiently. However, Huh-7 cells transfected with full-length genomes produce open reading frame 2 protein, indicative of genome replication (6). To investigate the role of 3'-terminal sequences in RNA replication, we constructed chimeric full-length genomes with divergent 3'-terminal sequences of genotypes 2 and 3 replacing that of genotype 1 and transfected them into Huh-7 cells. The production of viral proteins by these full-length chimeras was indistinguishable from that of the wild type, suggesting that replication was not impaired. In order to better quantify HEV replication in cell culture, we constructed an HEV replicon with a reporter (luciferase). Luciferase production was cap dependent and RNA-dependent RNA polymerase dependent and increased following transfection of Huh-7 cells. Replicons harboring the 3'-terminal intergenotypic chimera sequences were also assayed for luciferase production. In spite of the large sequence differences among the 3' termini of the viruses, replication of the chimeric replicons was surprisingly similar to that of the parental replicon. However, a single unique nucleotide change within a predicted stem structure at the 3' terminus substantially reduced the efficiency of replication: RNA replication was partially restored by a covariant mutation. Similar patterns of replication were obtained when full-length genomes were inoculated into rhesus macaques, suggesting that the in vitro system could be used to predict the effect of 3'-terminal mutations in vivo. Incorporation of the 3'-terminal sequences of the swine strain of HEV into the genotype 1 human strain did not enable the human strain to infect swine.

Complete sequence of a Kyrgyzstan swine hepatitis E virus (HEV) isolated from a piglet thought to be experimentally infected with human HEV

Hepatitis E virus (HEV) was identified by RT-PCR amplification with degenerate ORF2 primers in the stool of a piglet experimentally inoculated with a stool suspension from a patient with acute hepatitis during an outbreak of non-A, non-B hepatitis in Kyrgyzstan. Further characterization by sequencing of the complete genome and phylogenetic analysis showed that the piglet isolate was most closely related to HEV genotype 3. Because the original human stool specimen used to inoculate the piglet was no longer available, stool samples from three patients obtained during the same outbreak were sequenced and found to be HEV genotype 1. These findings suggest that the HEV isolated from the swine stool was probably an HEV enzootic in Kyrgyzstan and not the virus inoculated from the human stool.

An ELISA for putative neutralizing antibodies to hepatitis E virus detects antibodies to genotypes 1, 2, 3, and 4

Two monoclonal antibodies that neutralize hepatitis E virus (HEV) were used to identify a subregion of ORF2 capsid protein spanning amino acids 459-607 as the shortest peptide to form the corresponding neutralization epitopes. An enzyme-linked immunosorbent assay (ELISA) based on a purified recombinant protein covering amino acids 458-607 in ORF2 of the Sar-55 strain (genotype 1) efficiently detected anti-HEV in non-human primates which had been experimentally infected with the four known mammalian genotypes of HEV, respectively. However, anti-HEV in these animals did not react with a shorter ORF2 peptide spanning amino acids 475-607. The ELISA was highly specific and sensitive when human or non-human primate sera were tested in parallel with a previously established ELISA based on amino acids 112-607 in ORF2. The antibody titer to peptides 458-607 in two ORF2-vaccinated rhesus monkeys which had different HEV challenge outcomes differed at the time of challenge. Since the ELISA appeared to be specific for neutralizing antibodies against HEV, it should be especially useful for quantifying the humoral immune response in hepatitis E vaccine trials.

Evidence for hepatitis E virus quasispecies

The genetic diversity of hepatitis E virus (HEV) has been extensively analysed during the last decade. Most sporadic and epidemic HEV strains are distributed into genotypes or groups. Nevertheless, few studies have looked at the polymorphism of HEV strains isolated from a given outbreak. A serum bank collected in Tanefdour, Algeria, during an acute hepatitis epidemic (1986-1987), retrospectively confirmed as hepatitis E, was analysed. Of the 69 serum samples collected within an 8-week period, 23 were positive for both partial ORF1 (replicase gene) and ORF2 (capsid gene) sequences. Inter- and intra-patient diversities were assessed by RFLP, and by sequencing a 448 bp sequence corresponding to ORF2. RFLP analysis distinguished three profiles: A (18/23), B (3/23) and C (2/23). Most isolates (18/23) shared 99.7-100 % sequence identity and the remainder showed 1-1.3 % divergence. HEV intra-patient diversity was studied using 12 isolates (seven displaying the major RFLP profile and five displaying minor RFLP profiles). For 9 of 12 isolates, additional intra-patient heterogeneity was revealed by RFLP analysis of 100 clones from each isolate and sequence diversity ranging from 0.11 to 3.4 %. These data strongly support the quasispecies organization of HEV during epidemics and could explain the adaptable behaviour of the virus in the host-pathogen interrelations.

Identification of 5’ capped structure and 3’ terminal sequence of hepatitis E virus isolated from Morocco

AIM: To examine 5’ and 3’ terminal sequences of hepatitis E virus (HEV) isolated from Morocco, to confirm 5’ methylated cap structure of the genome, and to investigate whether the 3’ UTR can be used to distinguish HEV genotypes instead of HEV complete genome sequence.

METHODS: RNA ligase-mediated rapid amplification of cDNA ends (RLM-RACE) was employed to obtain the 5’ and 3’ terminal sequences of HEV Morocco strain. The 3’ UTR sequence of the Morocco strain was compared with that of the other 29 HEV strains using the DNAStar software.

RESULTS: The 5’ PCR product was obtained only from the RLM-RACE based on the capped RNA template. The 5’ UTR of the Morocco strain had 26 nucleotides, and the 3’ UTR had 65 nucleotides upstream to the polyA. The 5’ UTR between HEV strains had only point mutations of nucleotides. The phylogenetic tree based on the sequences of 3’ UTR was not the same as that based on the complete sequences.

CONCLUSION: The genome of HEV Morocco strain was methylated cap structure. The 3’ terminal sequence can not be used for distinguishing HEV genotype for all HEV strains in place of the whole HEV genome sequence.

Evidence for the presence of hepatitis E virus in pigs in the United Kingdom

Samples of serum, tissue and faeces from two pig herds in England were examined for hepatitis E virus by reverse-transcriptase PCR (RT-PCR), and a virus strain from each herd was partially sequenced. Eleven of 42 faecal samples and 16 of 21 tissue samples from two pigs were positive for the virus by RT-PCR. Analysis of two unique but closely related nucleotide sequences obtained from the two herds showed that the viruses clustered in genotype III (6) with a human strain of the virus from an autochthonously acquired case of acute hepatitis in the UK. An ELISA based on recombinant open reading frame 2 (ORF-2) was used to detect antibodies to hepatitis E virus in 256 pig sera from the UK; 85.5 per cent of the samples were positive, compared with 58 per cent of similar samples from Swedish pigs and 23.5 per cent of samples from Dutch pigs.

The ORF3 protein of hepatitis E virus interacts with liver-specific alpha1-microglobulin and its precursor alpha1-microglobulin/bikunin precursor (AMBP) and expedites their export from the hepatocyte

Hepatitis E virus (HEV), a plus-stranded RNA virus contains three open reading frames. Of these, ORF1 encodes the viral nonstructural polyprotein; ORF2 encodes the major capsid protein and ORF3 codes for a phosphoprotein of undefined function. Using the yeast two-hybrid system to screen a human cDNA liver library we have isolated, an N-terminal deleted protein, alpha(1) -microglobulin/bikunin precursor (AMBP) that specifically interacts with the ORF3 protein of HEV. Independently cloned, full-length AMBP was obtained and tested positive for interaction with ORF3 using a variety of in vivo and in vitro techniques. AMBP, a liver-specific precursor protein codes for two different unrelated proteins alpha(1)-microglobulin (alpha(1)m) and bikunin. alpha(1) m individually interacted with ORF3. The above findings were validated by COS-1 cell immunoprecipitation, His(6) pull-down experiments, and co-localization experiments followed by fluorescence resonance energy transfer analysis. Human liver cells showing co-localization of ORF3 with endogenously expressing alpha(1) m showed a distinct disappearance of the protein from the Golgi compartment, suggesting that ORF3 enhances the secretion of alpha(1)m out of the hepatocyte. Using drugs to block the secretory pathway, we showed that alpha m was not degraded in the presence of ORF3. Finally, (1)pulse labeling of alpha(1)m showed that its secretion was expedited out of the liver cell at faster rates in the presence of the ORF3 protein. Hence, ORF3 has a direct biological role in enhancing alpha(1)m export from the hepatocyte.

Protection of cynomolgus monkeys against HEV infection by oral administration of recombinant hepatitis E virus-like particles

Hepatitis E virus (HEV) is an important causative agent of enterically-transmitted hepatitis. Successful vaccine development is crucial in controlling global HEV infection. HEV capsid protein, with 111 amino acids truncated at the N-terminus, was efficiently expressed in the baculovirus expression system. Expressed protein spontaneously assembled into virus-like particles (VLPs) and was released into culture medium. When cynomolgus monkeys were orally inoculated with 10mg of purified rHEV VLPs, serum IgM, IgG, and IgA responses were observed. All these antibody responses were obtained without adjuvants. When the monkeys were challenged with native HEV by intravenous injection, they were protected against infection or developing hepatitis. These results suggested that recombinant HEV (rHEV) VLPs can be a candidate for the oral hepatitis E vaccine.

Genetic identification of avian hepatitis E virus (HEV) from healthy chicken flocks and characterization of the capsid gene of 14 avian HEV isolates from chickens with hepatitis–splenomegaly syndrome in different geographical regions of the United States

Avian hepatitis E virus (HEV), a novel virus identified from chickens with hepatitis-splenomegaly (HS) syndrome, is genetically and antigenically related to human HEV. Recently, it was found that avian HEV antibody is also prevalent in healthy chickens. A prospective study was done on a known seropositive but healthy chicken farm to identify avian HEV isolates from healthy chickens. Fourteen chickens were randomly selected, tagged and monitored under natural conditions for 19 weeks. All 14 chickens were seronegative at the beginning of the study at 12 weeks of age. By 21 weeks of age, all 14 chickens had seroconverted to avian HEV antibody. None of the chickens had any sign of HS syndrome. Partial helicase gene and capsid gene sequences of avian HEV isolates recovered from a healthy chicken were determined and found to share 75-97 % nucleotide sequence identity with the corresponding regions of avian HEV isolates from chickens with HS syndrome. Thus far, only one strain of avian HEV from a chicken with HS syndrome has been genetically characterized for its capsid gene, therefore the capsid gene region of an additional 14 isolates from chickens with HS syndrome were also characterized. The capsid genes of avian HEV isolates from chickens with HS syndrome were found to be heterogeneic, sharing 76-100 % nucleotide sequence identity with each other. This study indicates that avian HEV is enzootic in chicken flocks and spreads subclinically among chickens in the United States and that the virus is heterogeneic.

Use of heteroduplex mobility assays (HMA) for pre-sequencing screening and identification of variant strains of swine and avian hepatitis E viruses

Hepatitis E virus (HEV), the causative agent of human hepatitis E, is an important public health problem in many developing countries and is also endemic in many industrialized countries including the US. The discoveries of avian and swine HEVs by our group from chickens and pigs, respectively, suggest that hepatitis E may be a zoonosis. Current methods for molecular epidemiological studies of HEV require PCR amplification of field strains of HEV followed by DNA sequencing and sequence analyses, which are laborious and expensive. As novel or variant strains of HEV continue to evolve rapidly both in humans and other animals, it is important to develop a rapid pre-sequencing screening method to select field isolates for further molecular characterization. In this study, we developed two heteroduplex mobility assays (HMA) (one for swine HEV based on the ORF2 region, and the other for avian HEV based on the ORF1 region) to genetically differentiate field strains of avian and swine HEVs from known reference strains. The ORF2 regions of 22 swine HEV isolates and the ORF1 regions of 13 avian HEV isolates were amplified by PCR, sequenced and analyzed by HMA against reference prototype swine HEV strain and reference prototype avian HEV strain, respectively. We showed that, in general, the HMA profiles correlate well with nucleotide sequence identities and with phylogenetic clustering between field strains and the reference swine HEV or avian HEV strains. Field isolates with similar HMA patterns generally showed similar sequence identities with the reference strains and clustered together in the phylogenetic trees. Therefore, by using different HEV isolates as references, the HMA developed in this study can be used as a pre-sequencing screening tool to identify variant HEV isolates for further molecular epidemiological studies.

The ORF2 protein of hepatitis E virus binds the 5' region of viral RNA

Hepatitis E virus (HEV) is a major human pathogen in much of the developing world. It is a plus-strand RNA virus with a 7.2-kb polyadenylated genome consisting of three open reading frames, ORF1, ORF2, and ORF3. Of these, ORF2 encodes the major capsid protein of the virus and ORF3 encodes a small protein of unknown function. Using the yeast three-hybrid system and traditional biochemical techniques, we have studied the RNA binding activities of ORF2 and ORF3, two proteins encoded in the 3' structural part of the genome. Since the genomic RNA from HEV has been postulated to contain secondary structures at the 5' and 3' ends, we used these two terminal regions, besides other regions within the genome, in this study. Experiments were designed to test for interactions between the genomic RNA fusion constructs with ORF2 and ORF3 hybrid proteins in a yeast cellular environment. We show here that the ORF2 protein contains RNA binding activity. The ORF2 protein specifically bound the 5' end of the HEV genome. Deletion analysis of this protein showed that its RNA binding activity was lost when deletions were made beyond the N-terminal 111 amino acids. Finer mapping of the interacting RNA revealed that a 76-nucleotide (nt) region at the 5' end of the HEV genome was responsible for binding the ORF2 protein. This 76-nt region included the 51-nt HEV sequence, conserved across alphaviruses. Our results support the requirement of this conserved sequence for interaction with ORF2 and also indicate an increase in the strength of the RNA-protein interaction when an additional 44 bases downstream of this 76-nt region were included. Secondary-structure predictions and the location of the ORF2 binding region within the HEV genome indicate that this interaction may play a role in viral encapsidation.

Phylogenetic analysis of the first complete hepatitis E virus (HEV) genome from Africa

Hepatitis E virus (HEV) is globally distributed, transmitted enterically and between humans and animals. Phylogenetic analysis has identified five distinct HEV genotypes. The first full-length sequence of an African strain (Chad) is presented and compared to 31 complete HEV genomes available, including the fulminant hepatitis strain from India, swine strains and a strain from Morocco. The two African strains are more closely related to genotype 1 than to any other genotypes and together they possibly form a sub-genotype or sixth genotype. The first evidence for recombination between divergent HEV strains is presented.

Evidence that rodents are a reservoir of hepatitis E virus for humans in Nepal

Hepatitis E virus (HEV) is an important cause of enterically transmitted hepatitis in developing countries. Sporadic autochthonous cases of hepatitis E have been reported recently in the United States and other industrialized countries. The source of HEV infection in these cases is unknown; zoonotic transmission has been suggested. Antibodies to HEV have been detected in many animals in areas where HEV is endemic and in domestic swine and rats in the United States. There is evidence supporting HEV transmission between swine and humans. Nevertheless, HEV has not been detected in wild rodents. We tested murid rodents and house shrews trapped in Nepal's Kathmandu Valley, where hepatitis E is hyperendemic, for HEV infection. The most commonly trapped species was Rattus rattus brunneusculus. Serum samples from 675 animals were tested for immunoglobulin G against HEV by enzyme-linked immunosorbent assay; 78 (12%) were positive, indicating acute or past infection. Antibody prevalence was higher among R. rattus brunneusculus and Bandicota bengalensis than in Suncus murinus. Forty-four specimens from 78 antibody-positive animals had sufficient residual volume for detection of HEV RNA (viremia) by reverse transcription-PCR. PCR amplification detected four animals (9%; three were R. rattus brunneusculus and one was B. bengalensis) with viremia. Phylogenetic analysis of the four genome sequences (405 bp in the capsid gene) recovered showed that they were identical, most closely related to two human isolates from Nepal (95 and 96% nucleotide homology, respectively), and distinct from HEV sequences isolated elsewhere. These data prove that certain peridomestic rodents acquire HEV in the wild and suggest that cross-species transmission occurs, with rodents serving as a virus reservoir for humans.

Genetic characterization and sequence heterogeneity of a canadian isolate of Swine hepatitis E virus

Swine hepatitis E virus (HEV) is a newly identified potentially zoonotic agent that is possibly transmitted to humans from pigs. Swine HEV is prevalent in pig populations and does not cause abnormal clinical symptoms in infected pigs, further implicating a likelihood of a risk of transmission to humans by normal contact. To date in North America, only one strain of swine HEV (strain US swine) has been fully sequenced. In the present study, we identified a swine HEV isolate from pigs in Canada, designated the Arkell strain, and determined the full length of the genomic sequence. The genome of Canadian strain Arkell consisted of 7,242 nucleotides, excluding the poly(A) tail of at least 15 A residues. The genome contained three open reading frames (ORFs), ORF1, ORF2, and ORF3, which had coding capacities for proteins of 1,708, 660, and 122 amino acids, respectively. Comparative analysis of the full-length genomic sequence indicated that the sequence of strain Arkell was distinct from those of all other known HEV isolates by 13 to 27% and shared the highest degrees of identity with human HEV isolates US-1 and US-2, HEV isolate US swine, and the human and swine HEV isolates recently isolated in Japan. On the basis of sequence similarities and phylogenetic analyses, HEV strain Arkell was grouped into genotype 3. The sequence of the Arkell swine HEV isolate differed from those of HEV isolate US swine and HEV isolate Japan swine by 13 and 14%, respectively. To date, two isolates of swine HEV (isolates Arkell and SK3 [D. Yoo et al., Clin. Diagn. Lab. Immunol. 8:1213-1219, 2001]) have been identified in Canadian pigs, and their sequences also differ from each other by 11.8%. Our studies indicate that, as with human HEV strains, swine HEV isolates exhibit extensive genetic heterogeneity.

Heterogeneity and seroprevalence of a newly identified avian hepatitis e virus from chickens in the United States

We recently identified and characterized a novel virus, designated avian hepatitis E virus (avian HEV), from chickens with hepatitis-splenomegaly syndrome (HS syndrome) in the United States. Avian HEV is genetically related to but distinct from human and swine HEVs. To determine the extent of genetic variation and the seroprevalence of avian HEV infection in chicken flocks, we genetically identified and characterized 11 additional avian HEV isolates from chickens with HS syndrome and assessed the prevalence of avian HEV antibodies from a total of 1,276 chickens of different ages and breeds from 76 different flocks in five states (California, Colorado, Connecticut, Virginia, and Wisconsin). An enzyme-linked immunosorbent assay using a truncated recombinant avian HEV ORF2 antigen was developed and used to determine avian HEV seroprevalence. About 71% of chicken flocks and 30% of chickens tested in the study were positive for antibodies to avian HEV. About 17% of chickens younger than 18 weeks were seropositive, whereas about 36% of adult chickens were seropositive. By using a reverse transcription-PCR (RT-PCR) assay, we tested 21 bile samples from chickens with HS syndrome in California, Connecticut, New York, and Wisconsin for the presence of avian HEV RNA. Of the 21 bile samples, 12 were positive for 30- to 35-nm HEV-like virus particles by electron microscopy (EM). A total of 11 of the 12 EM-positive bile samples and 6 of the 9 EM-negative bile samples were positive for avian HEV RNA by RT-PCR. The sequences of a 372-bp region within the helicase gene of 11 avian HEV isolates were determined. Sequence analyses revealed that the 11 field isolates of avian HEV had 78 to 100% nucleotide sequence identities to each other, 79 to 88% identities to the prototype avian HEV, 76 to 80% identities to chicken big liver and spleen disease virus, and 56 to 61% identities to other known strains of human and swine HEV. The data from this study indicated that, like swine and human HEVs, avian HEV isolates are genetically heterogenic and that avian HEV infection is enzoonotic in chicken flocks in the United States.

Polyphyletic strains of hepatitis E virus are responsible for sporadic cases of acute hepatitis in Japan

Among 87 patients who were previously treated for acute hepatitis of unknown etiology between 1992 and 2001 at five hospitals in Japan, 11 (13%) patients were positive for immunoglobulin M-class antibodies to hepatitis E virus (HEV) by enzyme immunoassay and had detectable HEV RNA by reverse transcription-PCR with two independent sets of primers derived from well-conserved genomic areas in open reading frames 1 and 2. Clinical HEV infection was significantly associated with male sex (9 of 11 versus 29 of 76 patients [P < 0.01]) and older age (52 +/- 11 [mean +/- standard deviation] versus 41 +/- 17 years [P < 0.05]), and its prevalence differed by geographic region (6 to 25%), with a higher rate in the northern part of Japan. At admission, the 11 patients with HEV-associated hepatitis had elevated alanine aminotransferase levels of 914 to 4,850 IU/liter, and all but 1 had elevated bilirubin levels of 1.5 to 24.0 mg/dl. The 11 HEV isolates were of genotype III or IV and were segregated into three groups with intergroup nucleotide differences of 9.5 to 22.0%. Phylogenetic analysis revealed that four isolates of genotype III were closely related to a Japanese isolate, while the other four isolates of the same genotype were nearest those from the United States. The remaining three isolates were close to known isolates of genotype IV in China and Taiwan but shared less than 88% identity with them. These results indicate that multiple genotypes of HEV cocirculate in Japan and contribute to the development of sporadic acute hepatitis, with the prevalence differing by age, sex, and geographic region.

New perspectives on hepatitis E

The infectious agent causing epidemic non-A, non-B hepatitis was identified in 1983 from a human challenge experiment. The novel hepatitis E virus (HEV) subsequently was cloned in 1990 and the genome sequenced. HEV transmission is highly endemic in Asia, the Middle East, and Africa. Fecal contamination of drinking water is the most common mode of spread. Although usually asymptomatic, HEV infection can cause fulminant hepatitis. Recent studies indicate that hepatitis E may be a zoonotic disease, with pigs and possibly rats serving as reservoirs for human infection. A recombinant HEV vaccine is currently in phase III clinical trials. The characterization of the major types of viral hepatitis during the last 20 years illustrates how modern genetic technology has revolutionized research in infectious diseases. Within less than two decades of the discovery of HEV, its epidemiology has been described, serologic tests have been developed, and a candidate vaccine has been evaluated in clinical trials.